The present invention relates to an antenna assembly suitable for wireless transmission of analog and/or digital data, and more particularly to an antenna assembly for providing a conformal circularly polarized antenna.
Recent advances in wireless communications devices have renewed interest in antennas suitable for such systems. Several factors are usually considered in selecting an antenna for a wireless telecommunications device. Significant among these factors are the size, the bandwidth, and the radiation pattern of the antenna.
Currently, monopole antennas, patch antennas and helical antennas are among the various types of antennas being used in wireless communications devices. These antennas, however, have several disadvantages, such as limited bandwidth and large size. Also, these antennas exhibit significant reduction in gain at lower elevation angles (for example, 10 degrees), which makes them undesirable in some applications.
One type of antenna is an external half wave single or multi-band dipole. This antenna typically extends or is extensible from the body of a wireless communication device in a linear fashion. Because of the physical configuration of this type of antenna, electromagnetic waves radiate equally toward and away from a user. Thus, there is essentially no front-to-back ratio and little or no specific absorption rate (SAR) reduction. With multi-band versions of this type of antenna, resonances are achieved through the use of inductor-capacitor (LC) traps. With this antenna, gains of +2 dBi are common. While this type of antenna is acceptable in some wireless communication devices, it has drawbacks. One significant drawback is that the antenna is external to the body of the communication device. This places the antenna in an exposed position where it may be accidentally or deliberately damaged.
A related antenna is an external quarter wave single or multi-band asymmetric wire dipole. This antenna operates much like the aforementioned antenna, but requires an additional quarter wave conductor to produce additional resonances. This type of antenna has drawbacks similar to the aforementioned antenna.
Yet another type of antenna is a Planar Inverted F Antenna (PIFA). A PIFA derives its name from its resemblance to the letter xe2x80x9cFxe2x80x9d and typically includes various layers of rigid materials formed together to provide a radiating element having a conductive path therein. The various layers and components of a PIFA are typically mounted directly on a molded plastic or sheet metal support structure. Because of their rigidity, PIFAs are somewhat difficult to bend and form into a final shape for placement within the small confines of radiotelephones. In addition, PIFAs may be susceptible to damage when devices within which they are installed are subjected to impact forces. Impact forces may cause the various layers of a PIFA to crack, which may hinder operation or even cause failure. Various stamping, bending and etching steps may be required to manufacture a PIFA because of their generally non-planar configuration. Consequently, manufacturing and assembly is typically performed in a batch-type process which may be somewhat expensive. In addition, PIFAs typically utilize a shielded signal feed, such as a coaxial cable, to connect the PIFA with the RF circuitry within a radiotelephone. During assembly of a radiotelephone, the shielded signal feed between the RF circuitry and the PIFA typically involves manual installation, which may increase the cost of radiotelephone manufacturing.
An antenna assembly for a wireless communications device. The antenna assembly is mountable onto a printed wiring board (PWB) and consists of first and second conducting elements. The first conducting element is both capacitively coupled via a matchable shunt and operatively connected to a ground plane of the PWB, while the second conducting element is operatively connected to the ground plane of the PWB at two locations. The first and second conducting elements are operatively connected to each other by a tunable bridge capacitor to form orthogonal magnetic dipole elements. The antenna assembly provides substantially circular polarization within a hemisphere by virtue of the geometry and orientation of the two magnetic dipole elements which are fed with equal amplitude, but in-phase quadrature. The matchable shunt acts as an impedance transformer to yield a low voltage standing wave ratio (VSWR) of less than two-to-one at the operating frequency. The antenna assembly includes a single feed point which is capacitively coupled to and in parallel with the matchable shunt to ensure that the magnet dipole elements do not present a direct current (DC) ground to any radio frequency (RF) circuit connected to the antenna assembly. The single feed point permits RF energy to be distributed to both conducting elements without a required power splitter or phase shifter(s).
It is an object of the present invention to provide an antenna assembly which may be incorporated into a wireless communication device.
It is another object of the present invention to provide polarization diversity which can enhance radio performance in multipath environments, such as inside buildings or within metro areas.
It is yet another object of the present invention to provide frequency agility by adjusting the value of a bridge capacitor.
It is a further object of the present invention to enhance operation of an antenna assembly over a range of frequencies.
A feature of the present invention is the provision of orthogonally oriented magnetic dipole elements.
Another feature of the present invention is that there is a single feed point for radio frequencies.
Another feature of the present invention is that the antenna assembly is tunable over a range of frequencies.
An advantage of the present invention is that the antenna assembly has a low profile which enables it to be used in small articles such as wireless communication devices.
Another advantage of the present invention is that various components of a transciever device may be positioned within interior regions of the antenna assembly to reduce the overall size of the electronic device.
These and other objects, features and advantages will become apparent in light of the following detailed description of the preferred embodiments in connection with the drawings.